Anatomy of Eukaryotic Cells

Biology IIAnatomy & Physiology

Origin of Cellular Life• The Earth formed about 4.6 billion years ago.

o For about 500 million years, the Earth was continually bombarded by chunks of rock and ice in the solar system.

• The early atmosphere of Earth contained:o Water vapor H2Oo Nitrogen N2

o Carbon dioxide CO2

o Methane CH4

o Ammonia NH3

Origin of Cellular Life• How did life arise from such a harsh environment?• Two scientists designed a model of what conditions

were like on Earth at this time.o This is called the Miller-Urey Apparatus

Miller-Urey Apparatus• This apparatus

simulated three important conditions on Earth:– The high amount

of lightning– Heat and gases

released by volcanic activity

– Water vapor present in the atmosphere.

Results of Miller-Urey Apparatus

• Simple compounds including water (H2O), methane

(CH4), ammonia (NH3), and hydrogen (H2) were used to simulate the atmosphere.

• After 2 weeks, 10-15% of the carbon had been used to form sugars, amino acids, and parts of nucleic acids. o These simple organic compounds could have produced the

proteins, lipids, and carbohydrates that make up life today.

The First Cells• The first life forms on Earth were likely single-celled

prokaryotic organisms.• Prokaryotic organisms are single-celled

organisms that do not have a nucleus.o Their DNA or RNA is usually floating freely inside the cell.

• Prokaryotic cells also do not have any membrane bound organelles.

• Eukaryotes are organisms with much larger and more complex cells than prokaryotes.• DNA is in a nucleus that is

bounded by a nuclear membrane.

• Have membrane-bound organelles

• The largest eukaryotic cells are 0.1mm to 1.0mm in size. Why haven’t they evolved any larger?

Eukaryotic Cells

Total surface area(height x width xnumber of sides xnumber of boxes)

6

125 125

150 750

1

11

5

1.2 66

Total volume(height x width x lengthX number of boxes)

Surface-to-volumeratio(surface area volume)

Surface area increases whileTotal volume remains constant

• If the larger cell is instead broken down into 125 smaller cells, it will once again have enough surface area.

• This is why multicellular organisms exist!

The ostrich egg is one of the largest known single cells.

Cell Organization• The eukaryotic cell can be divided into two major

parts: the nucleus and the cytoplasm.• The nucleus is a separate compartment that

contains the DNA of the cell.• The cytoplasm is the fluid portion of the cell

outside the nucleus.o Prokaryotic cells have cytoplasm as well, even though they

do not have a nucleus.

Eukaryotic Cell Anatomy

• A eukaryotic cell has internal membranes that partition the cell into organelles.o Organelles are small structures within cells that have

specific jobs.

• Plant and animal cells have most of the same organelles, although there are a few differences.

Animal Cell Anatomy

Smooth Endoplasmic Reticulum

Cytoplasm

Vacuole

Centriole

Villi

Mitochondria

Nuclear Membrane

Golgi Apparatus

Nucleolus

Chromatin (DNA)

Nuclear Pores

Rough Endoplasmic Reticulum

Plasma Membrane

Lysosome

The Nucleus• The nucleus contains most of the cell’s genes and

is usually the largest organelle.• The nuclear envelope is a membrane that

encloses the nucleus, separating it from the cytoplasm.

• In the same way that the boss gives the orders to control a factory, the nucleus is the control center of the cell.

• The nucleus contains nearly all the cell’s DNA and, with it, the coded instructions for making proteins and other important molecules.

The Nuclear Membrane• The nuclear envelope is dotted with thousands of

nuclear pores, which allow material to move into and out of the nucleus.

• The nucleus mainly contains chromatin— the cell’s DNA instructions joined with proteins.

The Nuclear Membrane• The nucleus also contains a

small dense region called the nucleolus.

• The nucleolus produces ribosomes, which are needed to build proteins.

Organelles that Build Proteins

• Because proteins carry out so many of the essential functions of living things, a big part of the cell is devoted producing and transporting them.

• Proteins are synthesized on ribosomes, which can be found in two places:o Freely floating in the cytoplasmo Attached to the endoplasmic reticulum

Ribosomes: Protein Factories

• Ribosomes are particles made of RNA and proteino Ribosomes produce proteins by following coded

instructions that come from DNA. o Each ribosome is like a small machine in a factory, turning

out proteins on orders that come from its DNA “boss.”

Endoplasmic Reticulum

• The endoplasmic reticulum (ER) is a huge membrane that is connected to the nuclear membrane.

• There are two distinct regions of ER:o Smooth ER, which lacks ribosomeso Rough ER, with ribosomes studding its surface

Smooth Endoplasmic Reticulum

• The smooth endoplasmic reticulum:o Synthesizes lipidso Metabolizes carbohydrateso Stores calciumo Detoxifies poison

• The smooth endoplasmic reticulum does not contain any ribosomes, so it is unable to synthesize proteins.

Rough Endoplasmic Reticulum

• The rough ERo Holds ribosomeso Produces any proteins needed by the cell.

The Golgi Apparatus• The Golgi apparatus is a series of flattened

membrane sacs in the cytoplasm.• Functions of the Golgi apparatus:

o Modifies, sorts, and packages materials into transport vesicles for storage or transport out of the cell.

o A typical path for a protein produced by the cell:o Rough ER → Golgi → Cell membrane → Released by cell

LE 6-16-1

Nuclear envelope

Nucleus

Rough ER

Smooth ER

LE 6-16-2

Nuclear envelope

Nucleus

Rough ER

Smooth ER

Transport vesicle

cis Golgi

trans Golgi

LE 6-16-3

Nuclear envelope

Nucleus

Rough ER

Smooth ER

Transport vesicle

cis Golgi

trans Golgi

Plasma membrane

Organelles that Store, Clean Up, and Support

• These are organelles that help the cell maintain its shape, clean up wastes, and store material needed later.o Vacuoleso Lysosomeso Cytoskeleton

Vacuoles• Vesicles and vacuoles are membrane-bound sacs

that store many materials.• Plant cells often have one large central vacuole.

This fills with water, making the cell rigid.o When they are empty and dry, plants wilt!

Lysosomes• Lysosomes, formed by the Golgi, serve as the cell’s

cleanup crew.• A lysosome has a lower pH, and is full of enzymes that

can digest proteins, lipids, polysaccharides, and nucleic acids.o Can also breakdown old organelles so they can be re-used.

• Perioxisomes are similar to lysosomes, but are formed by the endoplasmic reticulum. o These break down hydrogen perioxide (H2O2), a dangerous by-

product of fatty acid digestion.

Animation: Lysosome Formation

H2O2 → H2 + O2

Enzyme: Catalase

Cytoskeleton• The cytoskeleton is a network of protein filaments

that give the cell shape.o Can also help transport materials across the cell.

• Centrioles are part of the cytoskeleton that help move chromosomes during cell division.

Organelles that Capture and Release

Energy• All life requires energy.• Organisms either can get their energy from sunlight

via photosynthesis, or by eating other organisms via cell respiration.

• Photosynthesis occurs in chloroplasts.• Cell respiration occurs in mitochondria.

Mitochondria• Mitochondria are the power plants of the cell. • They convert the chemical energy stored in food

into smaller molecules for the cell to use.• Mitochondria have two membranes, outer and

inner.• The inner membrane is folded up to increase the

amount of surface area to do chemical reactions.

Chloroplasts• Chloroplasts contain the green pigment

chlorophyll, as well as enzymes and other molecules that function in photosynthesis

• Chloroplasts are found in leaves and other green organs of plants and in algae

Plasma Membrane• The plasma membrane is a selective barrier.

o Allows passage of oxygen, nutrients into the cell, and waste out of the cell.

• The general structure of a biological membrane is a double layer of phospholipidso This allows the cell to control what goes in and

out.

How are Plant Cells Different?

• Chloroplasts and mitochondria present.

• Large, central vacuole instead of multiple small ones.

• Cell wall in addition to a cell membrane.

Cell Wall• The cell wall is made of cellulose and serves as

support and protection for the cell.• Animals do not have cell walls, but plants, fungi,

and algae do.• The cell wall is outside of the cell membrane.

Plants: Plasmodesmata

• The cell wall is so thick that oxygen, nutrients, water, and waste cannot travel easily through.

• Plasmodesmata are channels that perforate plant cell walls

• Through plasmodesmata, water and other small molecules can enter the cell.

Animals: Tight Junctions, Desmosomes, and Gap

Junctions• Although animal cells do not have cell walls, they also have

special structures within their cell membranes.• At tight junctions, membranes of neighboring cells are

pressed together, preventing leakage of extracellular fluid.o Example: Lining of small intestines

• Desmosomes (anchoring junctions) fasten cells together into strong sheetso Example: Layers of outer skin cells

• Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cellso Example: Cardiac muscle cells

Case Study: Food Poisoning

• Bacteria like E.coli, salmonella, and H. pylori release signals into intestinal cells, causing the break down of tight junctions.

• Once the tight junctions are gone, water is able to seep into the small intestine, causing diarrhea.

LE 6-31

Tight junctions preventfluid from moving across a layer of cells

Tight junction

0.5 µm

1 µm

0.1 µm

Gap junction

Extracellularmatrix

Spacebetweencells

Plasma membranesof adjacent cells

Intermediatefilaments

Tight junction

Desmosome

Gapjunctions

The Plasma Membrane• The plasma membrane is the boundary

that separates the living cell from its nonliving surroundings

• The plasma membrane exhibits selective permeability, meaning some substances can go through, others cannot.

• Plasma membranes are primarily made of phospholipids and proteins.

Phospholipids• A phospholipid is similar to a lipid, but one

of the fatty acids is replaced by a phosphate (PO4).

• The two fatty acid tails are hydrophobic, but the phosphate head is hydrophilic.

• When phospholipids are added to water, they self-assemble into a bilayero The phospholipids form the outer part that is

in contact with the water.o The fatty acids form the inner part that is

away from water.

WATERHydrophilic

head

WATER

WATERHydrophilic

head

Hydrophobictails

WATER

This phospholipid bilayer creates the basic structure of all cell membranes.

Fluid Mosaic Model• The fluid mosaic model states that a

membrane is constantly moving with a mixture of proteins embedded in it.

• As temperatures cool, membranes switch from a fluid state to a solid state

• Membranes must be fluid to work properly; they are usually about as fluid as vegetable oil.

LE 7-5b

Viscous (Thick)Fluid

Unsaturated hydrocarbontails with kinks

Saturated hydro-carbon tails

Membranes are fluid because they contain a high number of unsaturated fatty acids.

• Cholesterol helps to maintain the homeostasis of membranes, keeping them fluid.o At warm temperatures, cholesterol keeps

phospholipids from moving around too much.o At cool temperatures, it maintains fluidity by

preventing tight packing

Membrane Proteins• Proteins determine most of the membrane’s

specific functions• Peripheral proteins are on the surface of the

membrane, either outside or inside the cell.• Integral proteins go all the way through the

phospholipid bilayer and contact both sides.

• Six major functions of membrane proteins:1. Transport substances across the cell

membrane.

2. Serve as enzymes for reactions.

3. Receiving signals (e.g. hormones).

Membrane Proteins

4. Cell-cell recognition

5. Joining of two cells together

6. Attachment to the cytoskeleton

Membrane Proteins and Their Functions

Membrane Carbohydrates

• Cells can recognize each other by binding to carbohydrates on the plasma membrane.

• These carbohydrates vary among species, individuals, and even cell types in an individual.o This is how the immune system recognizes “self” and

“foreign” cells.o Example: Blood type (A, B, AB, O) is determined by markers

on your red blood cell membranes.

Permeability of the Lipid Bilayer

• The cell membrane is selectively permeable, meaning some molecules pass through, others cannot.

• Nonpolar (hydrophobic) molecules can dissolve in the lipid bilayer and pass through the membrane rapidlyo Examples: Oxygen, carbon dioxide,

hormones made of lipids• Large polar (hydrophilic) molecules, cannot

cross the membrane as easily.o Examples: Glucose, sucrose, proteins

Passive Transport• Diffusion is the movement of molecules

areas of greater concentration to areas of lower concentration.

• This is considered passive transport because no energy is required.

LE 7-11a

Molecules of dye Membrane (cross section)

WATER

Net diffusion Net diffusion Equilibrium

Diffusion of one solute

Molecules of solute gradually pass through the membrane, eventually reaching equilibrium.

LE 7-11b

Net diffusion Net diffusion Equilibrium

Diffusion of two solutes

Net diffusion Net diffusion Equilibrium

Osmosis and Water Balance

• Osmosis is the diffusion of water across a selectively permeable membrane

• The direction of osmosis is determined only by a difference in the concentration of solutes.o Solutes are substances dissolved in water,

like sugar or salts.• Water diffuses across a membrane from the

region of lower solute concentration to the region of higher solute concentration

LE 7-12Lower

concentrationof solute (sugar)

Higherconcentration

of sugar

Same concentrationof sugar

sugar molecules cannot pass

through pores, butwater molecules can

H2O

Osmosis

Water Balance of Cells Without Walls

• These are the three types of solutions that cells can be placed in:

• Isotonic solution: concentration of solutes (sugars, salts) is the same as that inside the cello cell does not change

• Hypertonic solution: concentration of solutes is greater outside the cello cell loses water and shrivels up

• Hypotonic solution: concentration of solutes is lower than that inside the cello cell gains water and bursts

Effect of Tonicity on Animal and Plant Cells

• Can you predict what will happen when a red blood cell is exposed to different types of solutions?

LE 7-13

Animalcell

Lysed

H2O

Distilled water Isotonic solution Saltwater

H2O

Shriveled

H2OH2OH2OH2OPlantcell

Turgid (normal) Flaccid Plasmolyzed

?

LE 7-13

Animalcell

Lysed

H2O H2O H2O

Normal

Distilled water Isotonic solution Salt water

H2O

Shriveled

H2OH2OH2OH2OPlantcell

Turgid (normal) Flaccid Plasmolyzed

?

LE 7-13

Animalcell

Lysed

H2O H2O H2O

Normal

Distilled water Isotonic solution Saltwater

H2O

Shriveled

H2OH2OH2OH2OPlantcell

Turgid (normal) Flaccid Plasmolyzed

?

LE 7-13

Animalcell

Lysed

H2O H2O H2O

Normal

Distilled waterIsotonic solution Salt water

H2O

Shriveled

H2OH2OH2OH2OPlantcell

Turgid (normal) Flaccid Plasmolyzed

?? ?

• Animal cells cannot survive in a hypertonic or hypotonic environment because their cell membranes are too thin.

• Some organisms have adaptations to allow them to survive in these environments.o Example: The protist Paramecium lives in a

hypotonic environment.• It has vacuole that can absorb excess water

and pump it back out of the cell.

LE 7-14

Filling vacuole50 µm

50 µmContracting vacuole

Water Balance of Cells with Walls

• Plant cells have cell walls. • Cell walls are thicker then plasma membranes

and do not burst. • This allows plants to survive in different

environments.

LE 7-13

Animalcell

Lysed

H2O H2O H2O

Normal

Saltwater solution Isotonic solution Distilled water

H2O

Shriveled

H2OH2OH2OH2OPlantcell

Turgid (normal) Flaccid Plasmolyzed

?

LE 7-13

Animalcell

Lysed

H2O H2O H2O

Normal

Hypotonic solution Isotonic solution Hypertonic solution

H2O

Shriveled

H2OH2OH2OH2OPlantcell

Turgid (normal) Flaccid Plasmolyzed

?

LE 7-13

Animalcell

Lysed

H2O H2O H2O

Normal

Hypotonic solution Isotonic solution Hypertonic solution

H2O

Shriveled

H2OH2OH2OH2OPlantcell

Turgid (normal) Flaccid Plasmolyzed

?

LE 7-13

Animalcell

Lysed

H2O H2O H2O

Normal

Hypotonic solution Isotonic solution Hypertonic solution

H2O

Shriveled

H2OH2OH2OH2OPlantcell

Turgid (normal) Flaccid Plasmolyzed

Facilitated Diffusion• In facilitated diffusion, transport proteins

aid movement of molecules across the plasma membraneo This increases the rate of transport.o This is considered passive transport because

no energy is used.

Transport Proteins• Channel proteins, act like a tunnel that ions or

other molecules can use to enter the cell.o Example: Aquaporins facilitate the passage of water.

• Carrier proteins, bind to molecules and change shape to shuttle them across the membraneo A transport protein is specific for one substance only.

Active Transport• Active transport moves substances

against their concentration gradient• Active transport requires energy, usually in

the form of ATPo ATP is the smallest, most basic energy-

containing molecule that cells use.• Active transport is performed by specific

proteins embedded in the membranes

Exocytosis• In exocytosis, transport vesicles from the

Golgi fuse with the cell membrane and release their contents to the outside.

Endocytosis• In endocytosis, the cell takes in large

molecules by forming vesicles from the plasma membrane

• Endocytosis is a reversal of exocytosis.